OBJECTIVES: 1. Past work by us has shown that the RNA of defective interfering (DI) particles of VSV (with one exception), contains an invariant 5'-terminal nucleotide sequence. It is proposed to sequence this region. This will be accomplished by annealing with sized fragments of the complementary mRNA fractionated on poly dT columns and polyacrylamide gels. Extracistronic sequences will be determined by ribonuclease T1 digestion of DI RNA hydrid with the whole mRNA. Also DNA probes will be used in sequencing. The latter will be prepared by copying the pertinent mRNA's with reverse transcriptase. The recently developed, faster DNA sequencing techniques will be used. 2. The mechanism by which an exceptional DI particle RNA, HR Indiana, interfered homotypically ad heterotypically will be investigated. Since the RNA of this particle contained the 3'-half of the viral genome, the nature of the promoter region at this end will be examined. Of interest is the inability of this RNA to be transcribed into mRNAs while it must be transcribed into a complete complementary strand as a prelude to replication. 3. A comparative study of the nature of DI particle RNAs in other rhabdoviruses is proposed in order to elucidate variations and similarities to the two types of autointerference found in VSV.